The present invention relates in general to a system of transferring an article to a load port and, more particularly, to a system of moving an article between a conveyor and a load port.
Automated transfer systems are used in a variety of applications to transport articles. The articles are typically loaded onto the transfer system using automated equipment which controls the flow of the articles. Automated equipment is also used to remove the articles at the exit point, with the transfer system and/or removal equipment being designed to allow several articles to accumulate near the contact point to prevent collisions between adjacent articles. With some applications, including semiconductor processing, the articles must be temporarily moved from the transfer system to a station, such as a work station, at one or more locations along the transfer system path. The articles are later returned to the transfer system, which then transports the articles to the next work station or the exit point. Moving the articles between the transfer system and work stations along the path can be complicated as care must be taken to ensure the transfer is accomplished without significantly interrupting the operation of the transfer system. A system for efficiently and conveniently transferring articles between a transfer system and a work station, without interfering with operation of the transfer system, is desirable.
One example of a field in which articles are temporarily removed from the transfer system at intermediate locations is the field of semiconductor processing. In this field, a transfer system may be used to transport semiconductor wafers or other substrates to several different processing machines. The wafers must be transferred to the machine for processing and, after processing has been completed, returned to the transfer system for delivery to the next processing machine. The wafers are typically retained in a protective container such as a sealed transport device or pod, to minimize any exposure of the substrates to the environment outside of the processing machines and protect the wafers against particulate contamination. The entrance of each processing machine is provided with a load port designed to automatically remove the wafers from the transport pod in a protected environment. During operation of the facility, transport pods must be frequently moved between the load port and transfer system.
Typically, the semiconductor manufacturing facility is organized into a plurality of bays each including several processing machines. Various systems are employed to move the transport pods between the machines within a bay. For example, many systems rely upon human workers to transfer the transport pods from port to port using a cart. The worker typically actuates a manual robotic link or other lifting device to move the pod to the port and, after processing has been completed, to return the transport pod to the cart. The process is repeated at the next machine. Another system of intra-bay transport relies upon automatic guided vehicles (AGVs) which carry the pods between the machines and automatically move the pods into the load port. The human propelled cart and AGV avoid the problem of transferring the pod to the load port without interrupting operation of the transfer system. However, the cart and AGV also lack the advantages associated with an automated transfer system, which can efficiently and rapidly move articles along a transfer system path.
Overhead transfer systems are also used to transport pods along the intra-bay loop. The pods are transferred to the load ports by hoists or similar devices which lower the pods onto the port. In order to successfully transfer the pod from the transfer system to the machine, the pod must be precisely aligned with the load port and lowered onto the port in a controlled manner such that any swing of the pod is minimized. After processing, the hoist or other device must engage the pod and lift the pod to the transfer system for transport to the next machine. Using a hoist or similar device to transfer the pod to the load port is complicated, and this method may be used only when the transfer system is positioned above the load port. The overhead transfer system can be difficult to maintain. Moreover, with the overhead transfer system, any particulate contamination or debris generated or carried by the transfer system will be introduced into the bay environment above the machines and load ports. Thus, there is a risk that these contaminants could fall or drift into the load port or other sensitive areas of the machines. Positioning the transfer system at the level of or below the load port reduces this risk. However, the hoist devices may not be used to transfer the pods to the load port from a transfer system which is positioned at or below the level of the port. A system for transferring an article to a workstation from a transfer system located in front of the load port is desirable.
Semiconductor wafers are delicate and, particularly in the later stages of processing, quite valuable. Integrated circuits are manufactured by forming a plurality of layers on a semiconductor wafer or other substrate. With advances in technology, integrated circuits have become increasingly complex and typically include multiple layers of intricate wiring. The number of integrated circuits positioned on a single wafer has increased due to the decreasing size of the integrated circuits. The standard size of the semiconductor wafers will increase from 200 mm to 300 mm or larger in the next few years, further increasing the number of integrated circuits which may be formed on a single wafer. As a result of the increased complexity and decreased size of the integrated circuits, the value of the semiconductor wafer increases substantially as the wafer progresses through the various processing stages. Thus, considerable care must be taken in handling the semiconductor wafers, particularly during the later processing stages, since damaged wafers could result in considerable monetary losses. The requirement of a clean room environment, substantially free of particulate contamination, for processing the wafers places further restraints on the systems which may be used to transfer the pods. A system for transferring articles between a transfer system and load port which is suitable for operation in a clean room environment is desirable.
A transfer system for moving articles, such as semiconductor wafers, transport pods carrying semiconductor wafers, or other containers, between a transfer system and a load port or other work station is desirable. A transfer system which may be used in field other than semiconductor processing, including but not limited to pharmaceuticals, medical systems, flat panel displays, computer hardware as for example disc drive systems, modems and the like, semiconductor wafers and lithography reticles is also desirable.
It is a primary object of the present invention to provide a system for transferring articles between a conveyor and a work station.
It is a further object of the present invention to provide a system for moving articles between a conveyor and a work station in a clean room environment.
It is another object of the present invention to provide a transfer system which may be used to automatically transfer articles between the conveyor and work station without significantly interrupting operation of the conveyor.
It is yet another object of the present invention to provide a transfer system for moving a transport pod or other container retaining a plurality of semiconductor wafers between a conveyor and the load port of a processing machine.
A more general object of the present invention is to provide a transfer system which may be efficiently constructed, operated and maintained, and is compatible with a variety of standard load ports.
In summary, the present invention provides a transfer system for moving an article between a conveyor and a station. For example, the article may be a transport device such as a pod or other container housing one or more articles (herein referred to in the singular as well as the plural) such as semiconductor wafers and the station may be a semiconductor processing machine or work station. Alternatively, the transfer system may be used to transport empty containers. The system includes a transfer assembly for moving the article. The transfer assembly generally includes a lifting mechanism configured to engage the article carried by the conveyor and lift the article to a raised position above the conveyor. The lifting mechanism is also configured to lower the article from the raised position to the conveyor when the article is returned. The transfer assembly also includes a displacement device configured to move the article from the raised position above the conveyor to a station, to position the article at the work station, and to return the article from the station to the raised position above the conveyor.
The transfer system of this invention also includes the method of transferring an article between a conveyor having a pair of spaced rails and a station positioned to one side of the conveyor. The method includes the steps of engaging the underside of the article between the rails and lifting the article to a raised position, and moving the article from the raised position to a position vicinal the station.
Additional objects and features of the invention will be more readily apparent from the following detailed description and appended claims when taken in conjunction with the drawings.